Global Review of Lake and Reservoir Eutrophication
and Associated Management Challenges
E. M. Mendiondo
Through a sequence of working questions, the
following sections outline a global review of
eutrophication of lakes and reservoirs with
associated management challenges. A short state-ofthe art on remedial measures and feasible
innovations to counterpart challenges enhances
yardsticks
of
decentralization
technologies,
ecohydrology issues, suitable scenarios to societal
goals, valuation of ecological services, trade-offs
meaningful for human well-being and lessons
learned for adaptive management. Consequently,
those topics are addressed towards governance,
management, research and capacity building in
order to assist stakeholders through sustainable,
accountable programs and win-to-win partnerships.
Eutrophication: a global problem
The growth of the human population in the first
decade of the 21st century is estimated as 100
million persons/year. Considering the per capita
production of 4g of phosphorus, 15g of nitrogen
and 100g carbon, as biological oxygen demand we
can get an insight into the eutrophication problems
that humanity has to face on a global scale.
Human waste and wastewater from the human,
agricultural and industrial activities will continue as
permanent inputs into lakes, rivers, reservoirs,
wetlands, coastal waters shallow lakes and coastal
lagoons. The causes and consequences of
eutrophication are well known, especially in temperate
waters (Jeppesen et al 2005). Effects to understand the
relationships of nitrogen and phosphorous loads and
the functioning on lakes, reservoirs and rivers (see
Box 1) under these stress conditions have been
intensified in the last 20 years (Sutcliffe and Jones
1992; UNEP/IETC 2001).
Eutrophication is thus a global problem aggravated by
contamination and other sources of pollution around
the world. The consequences of the deterioration of
the water bodies under eutrophication stress besides
the usual and well known impacts on the
biogeochemical and technological cycles in lakes and
reservoirs (Reynolds, 1992) are also of an economical
and social nature. These are not well measured or well
discussed consequences, but eutrophication has large
scale impact into the economy of entire regions as
well as in the social context quality of life and human
health (IETC 2001, Tundisi 2003).
Box 1. A short guide on global review of eutrophication
Increased input of nutrients, especially phosphorous, leads to an increased incidence of nuisance blooms
of blue-green algae, leading to a increase of water turbidity, a building of organic and nutrient-rich
sediments, loss of oxygen from the bottom waters of the lake which, in turn, accelerates nutrient
recycling processes, and changes in the lake’s food web structure. Secondary nutrient limitation of silica
or nitrogen that results when phosphorus levels are elevated also leads to changes in the phytoplankton
community and to the development of nuisance species of algae. Proliferation of macrophytes is
associated with eutrophication, especially in shallow lakes, but these problems are not tied directly to
excessive rates of nutrient loading. Although increases in nutrient levels enhance fish production, the
loss of habitat, e.g., by sediment buildup, deoxygenation, undesirable proliferation of macrophytes, and
food web simplification cause a shift from fish diversity to less desirable species, especially in more
extreme cases of eutrophication. Stocking of exotics and overfishing exacerbate this problem. From a
human use perspective these changes create numerous problems, i.e. fouling of boats and structures by
algal growths, loss of aesthetic appeal, accessibility problems for swimmers and boaters because of
macrophytes, economic damage to resort and property owners, and increased costs and technical
difficulties of treating water for drinking purposes because of taste and odor problems and increased
potential for trihalo-methane production. Once an oligotrophic lake has been made eutrophic,
processes develop that may delay recovery after nutrient loadings have been decreased. If the
hypolimnion becomes anoxic, recycling of phosphorous from the sediments is enhanced, in effect
increasing the efficiency of use of the phosphorous input. During the eutrophic phase many changes
may occur that will not be easily reversed by a reduction in nutrient supply, such a loss of desirable
macrophyte, invertebrate, and fish species. Source: adapted from NRC (1992), Tundisi (2003)
Global Review of Lake and Reservoir Eutrophication and Associated Management Challenges
Nutrient reduction is a necessary, but not always a
sufficient, condition for reversal eutrophy. Point
sources of nutrients are the primary cause of
excessive loadings in some lakes, but nonpoint
sources (urban and agricultural runoff) contribute
most of the nutrient input to the majority of lakes.
A further discussion is enclosed in the Box 2 which
depicts some of stresses. As consequence of this
process, on the one hand, eutrophication produces
a general reduction of possibilities of water use;
thus, the importance of reservoirs and lakes can be
compromised seriously as primary resources for
socio-economic development.
On the other hand, biological processes in
eutrophic environments increase productivity,
either as fish yield or as proteins’ source which
could be positively regarded for developing regions.
Thus, eutrophication involves increasing nutrient
inputs resulting from natural or human activities.
Since freshwater lakes or reservoirs become more
eutrophied, some ways to foresight and prevent
this problem was historically engineered through
the reduction and control of nutrients inputs.
Although this high-cost process is unquestionably
necessary in most of the cases, it does not produce
the expected improvement in a short-time –due to
the necessary adaptation time of the environment
to manage changes.
Where we go in terms of eutrophication
At the global scale since 1960 until 2005 the total
amount of freshwater stored in reservoirs grew up
four times. Although today’s reservoir freshwater is
three times bigger than in rivers, during the same
period the total loadings of nitrogen doubled and
phosphorous loadings tripled in water bodies.
Because most of these water bodies are located in
either tropical or subtropical regions, prospective
challenges of how to handle with eutrophication
growing is becoming a national level strategy, also in
transboundary frameworks and programs.
This calls a plea to stakeholders at temporal and spatial
scales. At temporal scales, the working hypotheses
outlined throughout the following sections depict a
summary of insights from eutrophication studies and
water practices that ought to share a plurality of
visions, analyses and projects worldwide. Those
hypotheses gather up the scientific methods applied
usually at short-term schedules, in compliance with
global societal demands, at long-term, through
demonstrative projects which put strengths in some
guidance questions and policy adaptation with
medium-term master plans.
At the spatial scales, associated management
challenges from remedial measures and possible
feasible innovations, either as structural or as nonstructural ones, are outlined at main spatial scales: of
the lake/reservoir and of the drainage basin. In real
cases, these scales have a continuum of integrated
scales of streams and rivers, wetlands and lake area.
The characteristics and emergent properties are
specific to each scale, but of common approach in
terms of restoration and stakeholder’s empowerment.
Also, structural and functional characteristics should
be assessed, as follows.
Structural features are water quality, geology and soil
condition, hydrology, topography, morphology, flora
and fauna, carrying capacity, food web support and
nutrient availability.
Functional features gather factors of surface and ground
water storage, recharge and supply, floodwater and
sediment retention, transport of organisms, nutrients
and sediments, humidification of atmosphere by
transpiration and evaporation, oxygen production,
nutrient cycling, biomass production, food web
support, and species maintenance, provision of shelter
for ecosystem users, detoxification of waste and
purification of water, reduction of erosion and mass
wastage, and energy flow. Most of them are related to
intrinsic possibilities of restoring water-bodies.
Box 2. Stresses affecting lake and reservoirs – becoming globally threaten?
Common stresses affecting lakes and reservoirs include eutrophication from nutrient and organic
matter loadings at local scales which provoke accumulated effects at long-term and global scales.
Siltation from inadequate erosion control in agricultural, construction, logging, or mining activities is
coupled with eutrophication; moreover, introduction of exotic species, acidification from atmospheric
sources and acid mine drainage can aggravate trophic states. And contamination by toxic or
potentially toxics metals such as mercury and organic compounds such as polychlorinated byphenyls
(PCBs) and pesticides are common downstream human settlements. Chemical stresses are
categorized according to source as (1) point sources, i.e. municipal wastewater, which generally are
the easiest to identify and control; (2) non-point or diffuse sources such as urban and agricultural
runoff from a lake’s watershed; and (3) long-range atmospheric transport of contaminants, which is
the most difficult to measure and control. These local stresses become cumbersome, because in the
last century the intercepted continental runoff grew up 15 times as urban center intensified.
Source: adapted from Millennium Ecosystem Assessment (2005).
Global Review of Lake and Reservoir Eutrophication and Associated Management Challenges
A review of restoration measures
In addition, physical changes both at the land-lake
interface by draining of riparian wetlands, and
hydrologic manipulations through damming outlets
to stabilize water levels also have major impacts on
the structure and functioning of lake ecosystems
(NRC, 1992). Some emergent properties for
restoration are (NRC, 1992; Mendiondo & Valdés,
2002): resilience, persistence, verisimilitude,
likelihood and adaptive management. Some
complementary definitions are enclosed in the Box
3, and their performance are broadly related to
management actions.
Lake-and-reservoir restoration is a relative recent
activity to attain global standards. Historically, the
term restoration has been applied broadly in lake
management to an array of actions aimed at
improving lake conditions for designated human
uses (e.g., contact, recreation, fishing, and water
supply). Return of a lake to its pristine condition
has note been an explicit goal of most lake
restoration projects, although these actions often
improve some aspects of a lake’s ecological
attributes. As such, most so-called lake restoration
projects are actually rehabilitation efforts, and many
are merely designed to manage (mitigate)
undesirable consequences of human perturbations.
It is worth noting a distinction between methods
that improve ecosystem structure and function
(restoration in the broad sense) and methods that
merely manage symptoms of stress. In the US, lake
restoration began after 1970, primarily in response
to problems of nutrient overenrichment (i.e. NRC,
1992).
For long-term restoration, it is essential to control the
source of the problem. In the case of eutrophication,
this means decreasing the loading of nutrients,
particularly phosphorous, from various watersheds
sources. In some cases, this also means that loadings of
silt and organic mater must be decreased.
Control of external sources is sufficient to return some
water bodies to their former conditions, but in many
cases the changes in the lake have been so dramatic –
major shifts in biota, loss of habitat, physical changes in
bottom sediments, and lake hydrology— that merely
turning off the loadings is not sufficient to improve
water quality and ecosystem structure, at least in a
reasonable time frame. In-lake restoration techniques
must be employed.
Numerous methods have been developed to restore
lakes or improve their conditions. Available methods
range widely in effectiveness, cost, frequency of use, and
range of applicability. Because eutrophication is the
most widespread and longest-studied lake problem,
more methods have been developed to restore
eutrophic lakes than to address all other problems put
together (NRC, 1992).
Limiting factors of eutrophication management
The common ability to assess the effectiveness of
management projects and to compare the performance
of restoration methods is severely limited by three
factors:
• continuous surveillance of lake conditions for an
adequate period of time before and after a
restoration attempt has been done on relatively few
lakes; sometimes, sufficient surveillance probably
was done, but analysis and interpretation of data
were not a part of the surveillance effort, or not
readily available to others;
Box 3. Brief description of managing water system features from local to global scales
Resilience is the ability of the ecosystem to recover from perturbation or to attain a new
equilibrium state after disturbance. Persistence, or self-sufficiency, is the ability of the system to
undergo natural successional process or persist in a climax sere (a stage in ecological succession),
without active human management; in short, persistence is the ability of the system to survive as a
dynamic system, evolving in a manner and at a rate regarded as normal for that type of ecosystem
at it particular stage of development (i.e. time between needed management intervention or units
of management effort required). Verisimilitude is a broad characteristic of the restored ecosystem
reflecting the overall similarity of the restored ecosystem to the standard comparison, be it prior
conditions of the ecosystem or of a reference system. Likelihood is the ability of the system to
produce non-linear, different responses within a confidence interval of possibilities, in front to the
same perturbation input. Adaptive management is a characteristic of restoration programs to assess
and survey measures in progressive ways in companion to natural reaction of system to changes in
time and in space.
Global Review of Lake and Reservoir Eutrophication and Associated Management Challenges
• restoration projects for lakes and reservoirs are
usually considered to be operational activities
rather than R&D projects; as a result they are
designated to produce the desired effect (a
restored water body) by whatever combination
of methods seems likely to succeed; it is so
usually not possible to determine which of
several techniques used simultaneously actually
produced the measured improvements, even if
detailed monitoring is done;
Restoration technology for lakes and reservoirs can be
advanced by ensuring that projects are monitored
adequately so that the effects of various manipulations
can been assessed properly. Some integrated
techniques seem promissory (Mendiondo, 2000;
Mendiondo & Valdés, 2002; Mendiondo et al, 2000a;
2000b), but further research should be developed to
validate at different biomes.
• the goals of restoration projects are not always
clearly defined, and it is difficult to judge the
degree of success when clear objectives have not
been set.
The measures for eutrophication control could be
structural, non-structural and a mix of them. High
loading of nutrients to lakes and reservoirs produces
algal blooms and other problems. In most cases,
oxygen-demanding organic matter, silt, toxic materials
accompany the nutrient loadings. Table 1 shows a
brief summary of restoration measures and their
convenience to main problems affecting lakes and
reservoirs. Restoration using the concept of
ecoregions – a major determinant of lake and
reservoir productivity is the steady-state, long-term
average concentrations of nutrients, especially those
that can be growth limiting, such as phosphorous,
nitrogen, and silica. For instance, control of algal
blooms consists, on the one hand, in:
• nutrient source reduction as actions towards
diversion, product modification, removal of
phosphorous from wastewater, interception of
nonpoint sources of nutrients, best management
practices, and dilution; or
• in-lake methods to reduce phosphorous
concentrations and cycling as phosphorous
inactivation, sediment skimming, sediment
oxidation, deep-water discharge as well;
• Management of symptoms as biomanipulation,
artificial circulation, algicides, among others.
Lake restoration projects typically focus on
restoring only one part (the lake) of a complex,
connected stream-wetland-lake system within a
watershed. When wetlands are considered at all in
lake restoration projects, it is currently for
diversion of nutrient-laden storm water runoff or
sewage effluent into the wetland in an effort to
obtain nutrient uptake by wetland vegetation. Such
diversions may provide a temporarily lowering of
nutrient loadings to lakes, but wetland flushing
during high flow periods may result in little net
annual retention of nutrients by the wetlands.
The impacts of diversion on wetland ecology
generally are not taken into account in deciding
whether to proceed with such project. Although
many techniques are potentially available to restore
degraded lakes, the science of lake or reservoir
restoration is still inexact, and the outcome of
applying a given technique to a particular lake is
difficult to predict accurately.
Local Measures
Box 4. Local ecological criteria for global successful measures
Water quality and human use criteria aided by use of simple trophic indices. The most widely
used TSIs are those developed by Carlsson, based on Secchi disk transparency and on
concentrations of total phosphate and chlorophyll a. An increase of 10 units in an index
represents a doubling of algal biomass. Carlsson recommended that the indices be considered
separately in evaluating trophic state. Lake morphometry plays a major role in determining the
amount of “internal loading” of nutrients from the sediments to the water column. Shallow
lakes, particularly those exposed to wind-induced mixing are likely to have high internal loading
rates. Water residence time also plays a role in determining lake water column nutrient
concentration. As water residence time decreases, the concentration of nutrients approaches
the concentration in incoming streams or rivers, and sedimentation of nutrients becomes less a
factor. Some controversies emerge about the success of restoration projects, as vested
interests, different standard of evaluation, or duration of evaluation period. Finally, success will
come whether some needs were addressed before as: continuous system restoration (river,
floodplain, lake/reservoir), the setting of restoration goal(s), the recognition of needs for
adaptive management and for improved assessments, and for high standard in assessing
functional equivalency (restored versus natural systems). Source: adapted from NRC (1992) and
Tundisi (2003)
Global Review of Lake and Reservoir Eutrophication and Associated Management Challenges
Table 1. Summary of local lake/reservoir restoration measures of eutrophication with suitability (“yes”) and
unsuitability or uncertainties (“?”) for the measure to each problem (adapted from NRC, 1992; Tundisi, 2003).
Exotic
Toxic
Structural measures
Eutrophication Siltation Acidification Species loads
yes
yes
Nutrient source reduction
yes
?
yes
Diversion
yes
yes
?
?
?
Land disposal
yes
?
?
?
?
Product modification
yes
?
?
?
yes
Wastewater treatment
yes
?
?
?
yes
Interception of nonpoint sources
yes
yes
yes
?
yes
Dilution
yes
?
yes
?
yes
Flushing
yes
?
yes
?
yes
In-lake methods
yes
?
yes
yes
yes
Alum treatment
yes
?
?
?
?
Sediment skimming
yes
?
?
?
yes
Sediment oxidation
yes
?
?
?
?
Deep-water discharge
yes
?
?
?
yes
Biomanipulation
yes
?
?
yes
?
Artificial circulation
yes
?
?
?
?
Biocides (algicides/herbicides)
yes
?
?
yes
?
Biocontrol agents
?
?
?
yes
?
Drawdown/sediment desiccation
yes
yes
?
?
?
Bioharvesting
yes
?
?
yes
?
Aeration
yes
?
?
?
?
Dredging
yes
yes
?
?
?
Liming
yes
?
yes
?
?
On the other hand, the control of aquatic
macrophytes encompasses biological agents, water
level drawdown, harvesting and herbicides. Finally,
to low dissolved oxygen some procedures include
hypolimnetic aeration and artificial aeration.
Reduction of nutrient loadings and related inputs
can be accomplished by (NRC 1992, Tundisi 2003):
• diverting point sources of nutrients or
nutrient-laden streams out of the lake’s
watershed,
• modifying products to contain lower amounts
of nutrients, mainly phosphorous;
• removing nutrients from wastewater in
engineered treatment systems;
• intercepting
nutrients
in
pre-lake
impoundments as stormwater detention and
retention ponds, natural or artificial wetlands;
• decreasing nutrient runoff from agricultural
lands by “best management practices”, and
• instituting land use and management controls.
Control methods for external sources of nutrients
encompass different situations:
• stream or wastewater diversion;
• municipality wastewater treatement (i.e.
tertiary treatment for N and P removal);
• product modification, i.e. legislative ban of
phosphate in laundry detergents, slow release
fertilizers);
•
treatment of
inflow streams, either as
diversion (into wetlands; over upland
vegetation)
or
in-stream
methods
(sedimentation/impoundment
basins
to
remove particulate N and P; channel aeration;
chemical precipitation; biotic harvesting).
The land use practices are discriminated by:
• prospective zoning (i.e. on-site storm at
retention or detention regulations; setback
and other shoreline restrictions on new
constructions; restrictions on shoreline
vegetation removal; restrictive zoning in
watershed
to
minimize
development;
minimization of impervious areas in
development; use of grassy swales instead of
curb and gutter drainage);
• best management practices: runoff controls to
change volume and peak flow through no or
minimum tillage; winter cover crop; contour
plowing and strip cropping; terraces; grassed
outlets; vegetated borders on fields and along
waterways; detention ponds;
• treatment of urban runoff, i.e. best management
practices (BMP) as retention/detention basins;
swirl concentrations; first flush diversion or
low flow to sanitary sewers;
• diversion of runoff into wetlands; street
sweeping or vacuuming; public education to
Global Review of Lake and Reservoir Eutrophication and Associated Management Challenges
•
reduce litter accumulation, to control lawn
fertilizer losses); or as treatment of
agricultural runoff
nutrient loss controls: timing and frequency of
fertilizer applications, their amounts and types
used; control in situ transformation of
fertilizers to soluble forms; crop rotation with
legumes; storage of manure during low
temperature season.
Integrated measures
One
cumbersome
problem
to
control
eutrophication is the complex nature of loadings
coupled to the flow regimes draining to the waterbodies. Figure 1 illustrates the example depicting
in Box 5 that several, equal possible scenarios of
loadings are possible to various levels of organic
matter production and with a wide range of
circumstances. In short, several combinations of
net productivity could attend dynamical, ecological
conditions of river flows, especially depending
upon water quality, becoming progressively more
complex to be managed if only at the
lake/reservoir scale. Another situation is to
estimate future treatment costs of water
withdrawals from lakes and reservoirs which river
basin will be under climate or land-use change (see
i.e. Box 6 and Figure 2).
Ecological features of freshwater biodiversity in
lake and reservoirs can be addressed over
landscape continuity through structural and
biological features of river corridors. This attempts
to ecohydrological categories which are detailed in
the Appendix 1, adapted from Mendiondo
(2008). All these categories are ranked in
accordance with principles of continuity, dynamics,
resilience, vulnerability and diversity in departure
of interactions among the drainage area, the
floodplain and the river. In this table, several
variables are defined in order to guide scientists
and water practitioners during the analysis of basic
data on field. In this way, the Appendix 2 also
points out an example of using the Appendix 1
through an interaction matrix between parameters,
as rows, and indicators through columns for urban
biodiversity responses to environmental stimuli
during flood pulses. In the Appendix 2 the arrow
direction points towards biodiversity increase,
having three potential biodiversity responses to
environmental stimuli: increase, decrease, and dual
response.
Associated management challenges
How challenges could be converted into
opportunities?
Here
is
briefly
depicted
prospectives to envisage challenges into
opportunities through yardsticks of technologies
towards eco-hydrology, to long-term scenarios
suitable to attain societal goals, to valuate of
ecological services of lakes and reservoirs, their
trade-offs meaningful for human well-being and
lessons learnt for adaptive management. Table 2
summarizes main questions for win-to-win
partnerships ranging from global to local scales.
Associated management challenges are crucial at
rivers, creeks and swamps connected to lakes and
reservoirs, highly dependant on budgets and
payment of environmental services. For instance, in
South American cases the average specific cost of
biodiversity restoration project in upper areas
should be up to US$ 2.5 million km-2 of drainage
area of river basin (Mendiondo, 2008b). For this
case, the average amount of environmental
services of subtropical rivers draining to reservoirs
are estimated from 28 to 33 million US$ km-2. This
figures point restoration projects as a small
amount in comparison with the benefits from lakes
and reservoirs. Project costs vary in a wide range
in dependence with the efficiency, the methods
used and the usage to evaluate costs per unit
drainage area or per river’s unit length.
Enhancement and rehabilitation costs differ from
restoration or renaturalization ones (Mendiondo,
1999). Enhancement-biodiversity projects cost ca.
3 U$ million km-1 of river length and 1.5 km-2 of
drainage basin. Conversely, restoration projects
rise to 25 U$ million km-1 of river, and
renaturalization can rise to more than 90 U$
million km-1 of river (Mendiondo, 2006). All these
costs support investment and maintenance during
the half life of the project to increase functions at
floodplain ecotones. These costs should be fully
compared with costs and efficiencies of water
treatment of eutrophication removal and, mainly,
with management frameworks suited with
stakeholders of the river basin. General speaking,
the higher river drainage area, the lower specific
costs per capita. This outlines needs for
hydrosolidarity trade-offs through implementing
river basin association to compensate the strong
degradation at upland areas with societal
management capacity at lowlands.
Thus some measures could be better addressed
through demonstrative pilot projects which help
on developing and setting a framework of sound
lake management for a continuing related research
agenda with policy and decision makers, lake users,
senior executives, Government officials, NGOs,
researchers and those who are involved in lakes &
reservoirs. Table 3 depicts one example of a
demonstrative pilot project based upon “Water for
Life” premises.
Global Review of Lake and Reservoir Eutrophication and Associated Management Challenges
Box 5 – Merging loadings and discharges to control eutrophication of lakes/reservoirs
Complentary to floods, the low-flow analysis of scenarios at river basins draining to a water-body
(Figure 1) is addressed comparing the duration of permanency (abscissa axis), average chlorophyll
balance of Productivity-to-Respiration ratio (P/R, in right ordinates) and specific discharges (left
ordinates). This chart is adequate to every size of river basin draining to a lake or reservoir and could be
used to make inferences about the sources of loads, either autochtonous or allochtonous of the river.
Indirectly, it also could be envisaged towards linking minimum flow needs of rivers to maintain various
equally possible states of in-stream biodiversity. In this figure, left ordinates, with solid lines, depict the
specific discharge of permanency curve with excedance probability in the abscissas. Right ordinates
outline different scenarios of specific chlorophyll-a loadings, related to the catchment area of the river, in
correspondence with the same probability values. The first scenario, with bold dotted lines, is related to
chlorophyll-a productivity higher than respiration (P / R >1) derived from the mixing process of
fitobenthos and alloctonous loads incorporated into the main flux of the river and during flood passages.
Conversely, during medium to low flows, the second scenario (with double continuous line) shows a
quasi steady-state, or quasi “lentic equilibrium”, without connection of the main river with adjacent
floodplain. In this second scenario of Figure 1, the net flux of chlorophyll-a remains constant (≈ 0.05 mg
s-1 Km-2) between 25% to 90% of permanency curve that corresponds to specific discharges ranging from
15 to 5 L s-1 Km-2). For this scenario, a decrease of net chlorophyll-a flux is expected for discharges
expected to occur for lower than Q90%, because of possible anoxic conditions and low radiation inputs.
When lentic behavior is persistent in time, without floodplain connections to river channel, a general
drop of chlorophyll-a net flux is expected for a new, third scenario (with double, non-continuous line).
This novel situation is characterized by a moderate reduction of the P/R ratio but with high
photosynthesis rates yet. However, if this situation persists with low photosynthesis rates, the P/R ratio
would maintain values below previous ones and consuming autoctonous organic matter, as showed in
the fourth scenario of Figure 1.
Source: Mendiondo (2008)
Figure 1- Flow analysis scenarios of river basin draining to a reservoir and with potential consequences to
trophic index, with discharge permanency (at abscissa axis), scenarios of average chlorophyll-a balance of
Productivity-to-Respiration ratio (four scenarios, at right ordinates) and specific discharges of permanency
curve (continuous line, at left ordinates). Source: Mendiondo (2008)
Global Review of Lake and Reservoir Eutrophication and Associated Management Challenges
Box 6. Treatment costs of water withdrawn from lakes/reservoirs under long-term change
Progressive loadings from rivers have persistent effects in trophic states which impact the future
treatment of water withdrawn from lake and reservoirs. These impacts could be addressed as the relative,
nominal change in treatment costs, i.e. the percentile difference of treatment costs between two
comparing periods related to the previous situation and for each time scale of the scenario. For instance,
in Figure 2 are depicted two long-term scenarios, both of them related to nominal treatment cost of
year 2000 and towards year 2025, 2050 and 2100. The first scenario (upper chart) points the expected
effect of the long-term climate change, and without land-use change in the upper river basin draining to
the water-body, in the treatment cost of water withdrawn and for different technologies of nitrogen and
phosphorous removal ranging from lower to higher efficiency methods: stabilization ponds,
natural/artificial wetlands as well as flocculation and denitrification. The second scenario (bottom chart) is
the expected treatment cost of water withdrawn for no climate change, but with land-use conversion at
the long-term between two scenarios: food and energy security, i.e. ethanol boom and cash-crops, in
comparison with ecotechnologies and payment for environmental services. Source: Mendiondo (2008a)
Figure 2. Nominal treatment costs (ordinates) expected for water withdrawn of water-body with different
trophic situation affected by long-term scenarios of time (abscissa) from only climate change (upper chart) or
only land-use conversion (bottom chart). Source: Mendiondo (2008,a)
Global Review of Lake and Reservoir Eutrophication and Associated Management Challenges
Table 2. Associated global management challenges for stakeholder’s empowerment
Keypoint
Working questions and hypotheses
Innovation
• What decentralized innovations are achievable to maintain the eco-hydrology of the system
“drainage basin & water body” as dynamic as developed?
• How could in-flow river needs help “catching” nutrients on basin floodplains to mitigate
downstream eutrophication of lakes/reservoirs?
Scenarios
• What consistent scenarios are suitable to attain goals of reducing eutrophication?
• How will the global change through scenario land-use assessment affect eutrophication of
lakes and reservoirs?
Ecological
Services
• How the ecological services of lakes and reservoirs could to be valuated?
• How do the degradation of ecosystem services at the basin (draining to a lake/reservoir)
cause significant harm (i.e. eutrophication) to human well-being?
Trade-offs
• How ecological services are meaningful for the human well-being?
Lessons learnt
• How past experiences “are”/ “should be” learned in perspective?
Transboundary
governance
• What yardsticks on eutrophication should underpin sustainability for stakeholder conflicts,
especially at trans-boundary river basins?
• Would ‘hydrosolidarity’ become a way to transboundary problems of eutrophication?
• Would potential pressure water conflicts make eutrophication accelerate at most?
Management
costs
• Which risks are to be coped with to avoid jeopardizing accountability?
• What insurance devices do cope with eutrophication risks at the long term through feasible
programs of early-warning?
• How could we propose protocols for regional water plans to better manage reservoirs
under, or in progress of, eutrophication at a global change?
• Could we regionalize the specific costs of today and future water demands on
reservoirs/lakes under progressive eutrophication?
• How does adaptive policy collaborate to maintain water quality at reservoirs (to decrease
eutrophication)?
Research
• How does it integrate eutrophication mitigation measures addressing ecohydrology?
• How does floodplain play as retention basin of nutrient loads?
• How to relate trophic factors with ecohydrology of floodplains?
Capacity
Building
• Where should ecosystem services empower the less resilient groups?
• How
could
early-warning
systems
assess
the
water
on incoming flows to lakes and reservoirs?
Pilot projects
.
Outlook
• What right actions to what most sensible audience?
Further agenda of global review of lake and
reservoir eutrophication should focus on some
detailed management challenges, as follows: (1) the
cost of eutrophication abatement, (2) the
differences of eutrophication in temperate and
tropical regions, (3) the emergence of
ecohydrology and ecotechnology opportunities,
and (4) the social and economic influences of
eutrophication to human well-being.
First, a problem that has not been considered for a
long time is the cost of abatement or
“compromise”
eutrophication control for feasible water treatment
costs. Considering structural and non structural
measures
eutrophication
control
has
a
considerable economic component derived
specially in the construction of infrastructure as
waste water treatment, plants, channels, etc and
organization of watershed or river basi committees
and their functioning. Therefore when controlling
eutrophication, it is necessary to consider these
costs, the technology used and the institutional
governance not only at the lake/reservoir scale but
also at the draining catchment area. If
transboundary situations appear, innovation and
negotiation are mandatory.
Global Review of Lake and Reservoir Eutrophication and Associated Management Challenges
Table 3. Example of a demonstrative pilot program to control and mitigate eutrophication of urban reservoir. Last line of the table depicts interval of costs of each phase
related to total project budget. Source: adapted from Mendiondo & Tundisi (2007) and Mendiondo (2008b)
Main Action
Detailed
actions and
products
(1)
Concept Paper &
Kick-off Policy
Workshop
(2)
Lifetime of Reservoir
through Technical
Assessment on Water
Security
(1.1)
Publishing the Whole
Strategy in a
Participative Workshop
with Stakeholders and
Decision-makers
(2.1)
In situ diagnosis of social,
economical, physical,
biological chemical,
cultural and institutional
variables.
(1.2)
“Water Security for
Life”; Motivation;
Problems;
Lessons Learned;
Stakeholders;
Goals
(2.2)
Integrated Models of:
society,
ecology,
sedimentology,
economics (insurance),
global change,
hydrology
(1.3)
Reflection:
Goals of “Water for
Life: 2010, 2020, 2030,
2050, 2100”, Actions;
Challenges; Chances;
Testimonies
(2.3) Scenarios:
institutional,
environmental
arrangements and water
security feasible at the
long-term
(2010 – 2100)
(3)
Value of Ecosystem
Services
(3.1)
Water Security with
Value of Ecosystem
Services of: Supporting
Provision;
Regulation;
Cultural
(3.2)
Permission of Services
for Security,
Life; Health; Social;
Human Well-Being
(3.3)
Willingness to Pay and
Prices of Services for:
Conflict Resolution and
Trade-offs
2 to 5
20 to 40
(4.1)
Structural Measures:
ecotechnology and ecohydrology towards
Ecosystem Services
Valorization
(4.2)
Non-Structural Measures
for Maintaining Services
until year 2010:
Tax Incentives;
Insurances;
Monitoring;
Early Warning;
River Association; PublicPrivate Partnerships;
Education & Training
(4.3)
Protocol of Institutional
Empowerment,
Governance, Policies and
Adaptive Management
until 2010.
(1.4)
Tutorial for next phases
Budget cost
(%)
(4)
Emergency Actions and
Short-term Mitigation
Strategies
10 to 12
Global Review of Lake and Reservoir Eutrophication and Associated Management Challenges
20 to 35
(5)
Policy Workshop &
Feedback Dialogue
on Water Security
Goals
(6)
TORs: Terms of
Reference on Security
& Eutrophication of
‘Water for Life’
(5.1)
Strategic, Multi-Sector
& Participative Goals
“2010, 2020 e 2030”
TORs of Demonstrative
Projects (scenarios, goals,
and actions):
Strategic Management;
(5.2)
Strategic Management
at the Long-Term;
Integrated Goals;
Identification of
Stakeholder (old and
new); Selection of
Indicators and Variables
(5.3) Implementation of
Initial Policies;
Assessment of Sets of
Indicators;
Methodology of
Hierarchy of Priorities
Institutional
Empowerment;
Risk Mitigation
& Conflict Reduction
Funding;
Incentive-driven Policies;
Social Inclusion;
Early Warning;
Sustainable Urbanization
Structural Measures
Capacity building
4 to 8
8 to 10
Second, the causes and consequences of
eutrophication of lakes and reservoirs are
approximately the same in temperate and tropical
lakes and reservoirs. However, the responses of
temperate waters differ in function of water
temperature, diversity, seasonality and succession
of species of the aquatic biota of these regions.
This makes difficult to introduce methods of
eutrophication control developed in temperate
regions to the tropical systems, especially when
considering in lake or reservoir management
technology. Trophic dynamics and role of fishes in
tropical warm waters differ considerably as stated
by Jeppensen et al (2005). Therefore techniques of
biomanipulation to control eutrophication in
temperate lakes many not apply directly to tropical
lakes. Therefore, it is necessary to develop a
strong research program on mechanisms of
functioning of tropical lakes and reservoirs under
eutrophication stress (Starling, 1993, Arcifa et al
1995; Tundisi & Tundisi, 2008).
Third, the progress of eutrophication of
continental and coastal waters in the last 25 years
was very fast with consequences on the functioning
of lakes and reservoirs worldwide. Economic and
social consequences of eutrophication have bean
dealt with in some regions, but is necessary an
effort to include these approaches (IETC 2001) in
the next steps to attempt to solve the problem.
The control of the eutrophication process starts in
the watershed and the ecotechnological and
ecohydrological technologies for this control is an
essential action. Without a watershed control with
new and cheaper techniques it will be impossible
to delay the consequences of eutrophication.
Finally, another emerging approach related to
eutrophication
and
its
control
is
the
epidemiological studies related to global impacts on
human health especially related with toxins from
algal blooms and their health consequences to
megacities and human settlement.
Acknowledgements
This short term report is prepared under the contract
from International Lake Environment Committee
Foundation, Shiga, Japan for developing contents for
training classes for lake basin managers under JICA
(Japan International Cooperation Agency) Project. The
views expressed and any errors are entirely those of the
author and do not necessarily conform to policy
viewpoints by the contacted individuals and institutions.I
thank Dr. Masahisa Nakamura, Professor, and Research
Center for Sustainability and Environment, Shiga
University for his interest in the author’s presentation
and Dr Thomas Ballatore, ILEC, for their kind invitation
and helping comprehension.
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Global Review of Lake and Reservoir Eutrophication and Associated Management Challenges
Appendix 1- Ecohydrological categories for sustainable river management to reduce eutrophication at lakes and reservoirsw (from Mendiondo, 2008b)
Category
Continuity
Diversity
Dynamics
Resilience
Vunerability
Interaction
Drainage area ↔ river
Drainage area ↔ river
Drainage area ↔ floodplain
Floodplain ↔ river
Floodplain ↔ river
Indicator associated to
number and extension of
drainage network and
frequency of floodplain
inundations, regarded to river
perenization and integration
processes between surface
and ground-waters and autodepuration at macro-scale.
Quantification of
permanently-flooded areas
with respect to potential
flood areas, as an indicator of
proportion of internal lentic
systems which potentially
exchange nutrients, energy
and information with the
main river channel.
Non-linear mechanisms of
multivariate processes of
nutrients, of information and
of energy transferred under
either limnophase or
potamophase stages.
Potential recovery capacity
to attain a new system
equilibrium under inputs of
matter, energy and
information
Risk analysis and
management of flood prone
areas with factors of: hazard
(return period), vulnerability
(indirect costs of loss or
excess of ecosystem service)
and exposition (relative
location inside flooplain to
main river channel).
X1: number of draining subbasins per unit of main
river channel length
[No./km]
X6: quotient of instantaneous
flooded areas, with regard
to total floodplain area
[km2/km2, %]
X2: density of drainage
streams per unit area
[km/km2]
X7: fraction of total
floodplain area and
upslope drainage basin
area [km2/km2, %]
X9: quotient of maintenance
time of flooded areas
after the occurrence of
maximum discharge and
the duration of flood
pulse [min./min., %]
X11: time rate of the
difference of primary
production, between
preserved and
degraded areas at
floodplain,
[g
Biomass/hours]
X15: difference of primary
production ‘during’ and
‘after’ maximum water
inundation, in relation
with primary production
‘before’ inundation [g/g,
%]
X12: time rate of river flow
per water level (i)
before, and (ii) after
flooding [m3/s/m]
X16: changes of permanency
flows of Q5% and
Q95%, from urban
impacts [m3/s]
X13: dimensional surface of
loops of primary
production indicator
versus total water level
X17: change of probability
values of 95%, from
urban impacts
[Probability],
X14: dimensional surface of
loops of primary
production indicator
versus water levels
above inundation
floodplain terrace
X18: multiplication of mean
velocity times water
level height [m2/s]
Indicator
[Definition]
Variable
[dimension]
X3: frequency of occurrence
of complete inundation of
flooplain [No./decades]
X4: fraction of permanent,
shallow water pools inside
floodplain [km/km2, %]
X8: number of different landuses per unit of floodplain
area [No/km2]
X10: fraction of inundation
duration above bankfull
water level and total flood
pulse [min./min, %]
X5: relation of potential
wetted perimeter of
maximum floodplain
cross-section and river
channel wetted perimeter
[m/m, %]
Global Review of Lake and Reservoir Eutrophication and Associated Management Challenges
Appendix 2- Interaction matrix between parameters (rows) and indicators (columns) for biodiversity responses to environmental stimuli during flood pulses at uplands
(defined in Appendix 1) which control lake and reservoir eutrophication downwards. Arrow direction points towards biodiversity increase.
Parameter
Category and indicators
(dimensions)
Continuity
Diversity
Dynamics
Resilience
Vulnerability
X1↑
X2↑
X3↑
X4↑
X5↑
X6↑
X7↑
X8↓
X9↑
X10↕
X11↑
X12↕
X13↕
X14↕
X15↕
X16↓
X17↓
X18↓
Q95%
++
++
?
+
+
++
+
?
++
--
++
w/r
?
?
?
-
--
-
Q50%
+
+
?
+/-
+/-
+
+
?
+
-
+
w/r
+/-
?
?
+/-
?
+/-
Q05%
+/-
+
++
+/-
-
+/-
-
+/-
+/-
+
+/-
+;-
+/-
+/-
-
+/-
?
+
Q01%
+/-
+/-
+
-
--
-
--
+/-
-
++
-
++;--
-
-
--
+
+
++
EC (µS/cm)
-
-
-
+/-
+/-
+/-
-
++
+/-
+/-
-
-;+
-
-
-
-
+
-
DOC (mg/L)
-
-
-
+/-
-
-
-
+
-
+/-
?
-;?
-
-
?
-
+
-
BOD (mg/L)
-
-
-
+/-
+/-
+/-
-
+
+/-
+/-
-
-;+
-
-
-
-
+
-
N-tot (mg/L)
+/-
+
-
+/-
+
+/-
+/-
+
+
-
+
+;-
?
?
?
+
++
+/-
P-tot (mg/L)
+
+/-
-
+/-
+
+/-
+/-
+
+
-
+/-
+;-
?
?
?
++
++
+/-
+/-
+/-
-
+
+
+/-
+
+/-
+
-
+
+;+
+
+/-
-
--
-
-
ISS (mg/L)
+
+
+
-
-
+
-
+
-
+
-
+;+
?
?
?
+
++
+
OSS(mg/L)
+
+
+
+/-
-
-
-
+
-
+
-
+;+
+/-
?
+
+
+
?
TSS(mg/L)
+
+
+
-
--
+/-
--
++
--
++
--
+;+
+/-
?
?
++
++
+
Biomass(g/m2)
Notation: Q95%: river flow discharge of expected permanency of 95% of annual river regime duration; EC: electric conductivity; DOC : dissolved organic carbon; BOD: biological
organic demand; N-tot: total nitrogen; P-tot: total phosphorous; ISS: inorganic suspended solids; OSS: organic suspended solids; TSS: total suspended solids.
Biodiversity responses to environmental stimuli ‘↑: increase’, ‘ ↓: decrease’ , ‘ ↕: dual response’; Interactions expected: ‘ + : positive, ‘+ +: high positive’ , ‘ - : negative, ‘- - : highly
negative’ , ‘ +/- : mixture’ ,‘ x ; x : rising limb , recession of flooding’, ‘? : indeterminate’, ‘w/r’: without relation
Global Review of Lake and Reservoir Eutrophication and Associated Management Challenges